Scroll compressor

ABSTRACT

A scroll compressor includes a fixed scroll member fixed to a housing and a movable scroll member engaging the fixed scroll member. Each scroll member has a base plate and a spiral wall. A compression chamber between the fixed and movable scroll members reduces in volume by orbiting the movable scroll member, thus compressing gas. A back pressure chamber is defined in the housing on a back surface side of the movable scroll base plate between the movable scroll member and the a fixed wall of the housing. An introducing passage interconnects the back pressure chamber and a relatively high pressure region. A seal member on one of the movable scroll member and the fixed wall seals the back pressure chamber as being slidable on the other. The seal member includes a portion for lowering sealing performance, which interconnects the back pressure chamber and a relatively low pressure region.

[0001] The present invention relates to a scroll compressor of arefrigeration cycle in a vehicle air conditioner for compressingrefrigerant.

[0002] A scroll compressor of such type includes a fixed scroll memberand a movable scroll member. The fixed scroll member has a spiral walland a base plate, and is fixedly connected to a housing of thecompressor. The movable scroll member has a spiral wall and a baseplate, and is engaged with the spiral wall of the fixed scroll member.As the movable scroll member orbits, compression chambers definedbetween both the spiral walls progressively reduce in volume, thuscompressing refrigerant gas.

[0003] Recently, carbon dioxide is employed as refrigerant for therefrigeration cycle. When carbon dioxide refrigerant is employed,pressure in the refrigeration cycle becomes much higher than that whenfluorocarbon refrigerant is employed. Accordingly, in the scrollcompressor, relatively large thrust load based upon pressure in thecompression chambers is applied to the movable scroll member. Thus, themovable scroll member slides under relatively hard condition, so thatreliability of the scroll compressor is deteriorated.

[0004] In order to solve such a problem, for example, as disclosed inUnexamined Japanese Patent Publication No. 2000-249086, the back surfaceof the movable scroll member is recessed to form a pocket for applyingback pressure, and the pocket for applying back pressure is shut by afixed wall provided in a housing of the compressor. Thus, a backpressure chamber is formed. A volume-reducing compression chambercommunicates with the back pressure chamber through an introducingpassage. Accordingly, force (force based upon the back pressure) thatresists against force (thrust load) based upon pressure in thecompression chambers is applied to the movable scroll member due to thepressure in the back pressure chamber, so that sliding resistance isreduced between the movable scroll member and the fixed wall.Additionally, the movable scroll member is pressed against the fixedscroll member, so that sealing performance of the compression chambersimprove.

[0005] The pressure in the back pressure chamber is appropriatelyadjusted by variation in the amount of a clearance (passingcross-sectional area) between the movable scroll member and the fixedscroll wall. In other words, for example, as the pressure in the backpressure chamber rises, the clearance between the movable scroll memberand the fixed wall increases. Accordingly, the amount of refrigerant gasdelivered from the back pressure chamber to a relatively low pressureregion through the clearance increases, so that an excessive rise in thepressure in the back pressure chamber is prevented. On the contrary, asthe pressure in the back pressure chamber falls, the clearance betweenthe movable scroll member and the fixed wall reduces. Accordingly, theamount of refrigerant gas delivered from the back pressure chamber tothe relatively low pressure region through the clearance reduces, sothat undesirable reduction in the pressure in the back pressure chamberis prevented.

[0006] An unwanted feature is that in accordance with the UnexaminedJapanese Patent Publication No. 2000-249086, the entire clearancebetween the movable scroll member and the fixed wall is utilized as apassage for delivering the refrigerant gas from the back pressurechamber to the relatively low pressure region. Accordingly, in order tooptionally and appropriately adjust the pressure in the back pressurechamber by the variation in the amount of the clearance, for example, afacing surface of the movable scroll member and a facing surface of thefixed wall need be manufactured in high accuracy. As a result, cost formanufacturing the scroll compressor rises.

[0007] Particularly, when carbon dioxide refrigerant is employed, thepressure in the back pressure chamber is adjusted in a much higher rangethan that when fluorocarbon refrigerant is employed. Accordingly, inorder to appropriately adjust the pressure in the back pressure chamber,the clearance between the movable scroll member and the fixed wall needbe much narrower at the maximum. Thus, a rise in cost for manufacturingbecomes a further serious problem. Therefore, there is a need forproviding a scroll compressor that has a reasonable structure andoptionally and appropriately adjusts pressure in a back pressurechamber.

SUMMARY OF THE INVENTION

[0008] In accordance with the present invention, a scroll compressor hasa housing, a fixed scroll member, a movable scroll member and a sealmember. The housing includes a fixed wall, and defines a relatively highpressure region and a relatively low pressure region. The fixed scrollmember has a base plate and a spiral wall extending from the base plate,and is fixedly connected to the housing. The movable scroll member has abase plate and a spiral wall extending from the base plate, and isengaged with the fixed scroll member. A compression chamber definedbetween the fixed scroll member and the movable scroll memberprogressively reduces in volume by orbiting the movable scroll memberrelative to the fixed scroll member, thus compressing gas. The backpressure chamber is defined in the housing on a back surface side of thebase plate of the movable scroll member between the movable scrollmember and the fixed wall. The back pressure chamber and the relativelyhigh pressure region are interconnected through an introducing passage.A seal member is provided on one of the movable scroll member and thefixed wall for sealing the back pressure chamber as being slidable onthe other of the movable scroll member and the fixed wall. The sealmember includes a seal lowering portion for lowering sealingperformance. The seal lowering portion interconnects the back pressurechamber and the relatively low pressure region.

[0009] Other aspects and advantages of the invention will becomeapparent from the following description, taken in conjunction with theaccompanying drawings, illustrating by way of example the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The features of the present invention that are believed to benovel are set forth with particularity in the appended claims. Theinvention together with objects and advantages thereof, may best beunderstood by reference to the following description of the presentlypreferred embodiments together with the accompanying drawings in which:

[0011]FIG. 1 is a longitudinal cross-sectional view of an electriccompressor according to a preferred embodiment of the present invention;

[0012]FIG. 2 is a rear end view of a movable scroll member, which isdetached from the scroll compressor, according to the preferredembodiment of the present invention;

[0013]FIG. 3A is a partially enlarged cross-sectional view around a sealmember of FIG. 1;

[0014]FIG. 3B is a partially enlarged cross-sectional view illustratinga state when a passing cross-sectional area of a portion for loweringsealing performance becomes small;

[0015]FIG. 4 is a rear end view of a movable scroll member according toan alternative embodiment of the present invention; and

[0016]FIG. 5 is a partially enlarged cross-sectional view of a relevantportion of an electric compressor according to an alternative embodimentof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] A preferred embodiment of the present invention will now bedescribed with reference to FIGS. 1 through 3B. In the preferredembodiment, a scroll compressor according to the present invention isapplied to an electric compressor for use in a refrigeration cycle of avehicle air conditioner. Incidentally, carbon dioxide is employed asrefrigerant of the refrigeration cycle. The left side and the right sideof FIG. 1 respectively correspond to the front side and the rear side ofthe electric compressor.

[0018] As shown in FIG. 1, a housing 11 of the electric compressorincludes a first housing element 21 and a second housing element 22. Thefirst housing element 21 and the second housing element 22 are fixedlyconnected with each other. The first housing element 21 has acylindrical portion 23 and a bottom portion 24, which connects with therear end of the cylindrical portion 23 (on the right side of FIG. 1).Thus, the first housing element 21 forms a cylinder with a bottom at oneend and is formed by die-casting an aluminum alloy. The second housingelement 22 forms a cylinder with a bottom on the front side (the leftside of FIG. 1) and is formed by die-casting an aluminum alloy.

[0019] A cylindrical shaft support portion 24 a extends from the centerof an inner wall surface of the bottom portion 24 in the first housingelement 21. A shaft support member 32, which has an insertion hole 32 aformed through the center thereof, is fixedly connected to an openingend of the cylindrical portion 23 in the first housing element 21. Arotary shaft 33 is accommodated in the first housing element 21. Therear end (the right end) of the rotary shaft 33 is rotatably supportedby the shaft support portion 24 a of the first housing element 21through a bearing 34. The front end (the left side) of the rotary shaft33 is inserted through the insertion hole 32 a of the shaft supportmember 32, and is rotatably supported by the shaft support member 32through a bearing 35 in the insertion hole 32 a.

[0020] A motor chamber 12 is defined in the housing 11 and is located onthe rear side of FIG. 1 relative to the shaft support member 32. In themotor chamber 12, a stator 36 is provided on the inner circumferentialsurface of the cylindrical portion 23 of the first housing element 21.In the motor chamber 12, a rotor 37 is secured to the rotary shaft 33 soas to be located inside the stator 36. The stator 36 and the rotor 37constitute the electric motor 13. The electric motor 13 integrallyrotates the rotor 37 and the rotary shaft 33 by electric powerexternally supplied to the stator 36.

[0021] A fixed scroll member 41 is accommodated in the first housingelement 21 and is located near the opening end of the cylindricalportion 23. The fixed scroll member 41 includes a disc-shaped base plate61, a cylindrical outer circumferential wall 62 and a spiral wall 63.The outer circumferential wall 62 extends from the outer periphery ofthe base plate 61. The spiral wall 63 extends from the base plate 61 andis located inside the outer circumferential wall 62. In the firsthousing element 21, a disc-shaped center frame or a fixed wall 31 isarranged between the fixed scroll member 41 and the shaft support member32. A through hole 31 a is formed through the center of the center frame31. An annular contact portion 31 b is located at the opening end nearthe motor chamber 12 in the through hole 31 a and protrudes inward.

[0022] The fixed scroll member 41 is connected to the outer periphery ofthe center frame 31 by the distal end surface of the outercircumferential wall 62. An annular shim 68 is interposed at a jointbetween the fixed scroll member 41 and the center frame 31. The baseplate 61 of the fixed scroll member 41, the outer circumferential wall62 of the fixed scroll member 41 and the center frame 31 surround todefine a scroll chamber 15 in the housing 11.

[0023] A crankshaft 43 is provided at the end surface of the rotaryshaft 33 near the center frame 31. The crankshaft 43 is mostly arrangedin the through hole 31 a of the center frame 31. A bushing 44 is fixedlyfitted around the crankshaft 43. A movable scroll member 45 isaccommodated in the scroll chamber 15 and is rotatably supported on thebushing 44 through a bearing 46 so as to face the fixed scroll member41.

[0024] A balancer 44 a is provided at the end of the bushing 44 near theshaft support member 32. The balancer 44 a relieves imbalance on therotary shaft 33 due to uneven arrangement of the movable scroll member45 around an axis L of the rotary shaft 33. The balancer 44 a isaccommodated in a balancer chamber 14 outside the through hole 31 a. Thebalancer chamber 14 is defined between the shaft support member 32 andthe center frame 31. The balancer chamber 14 communicates with the motorchamber 12 through a clearance of the bearing 35. Accordingly, thebalancer chamber 14 has the same atmospheric pressure as that of themotor chamber 12.

[0025] The movable scroll member 45 includes a disc-shaped base plate 65and a spiral wall 66 that extends toward the fixed scroll member 41. Aboss 67 is provided near the center of a back surface of the base plate65 and protrudes therefrom. The boss 67 is fitted around the bushing 44through the bearing 46 in the through hole 31 a of the center frame 31.An annular tip seal 77 is provided at the distal end of the boss 67. Inthe through hole 31 a, the boss 67 slidably contacts with the contactportion 31 b of the center frame 31 by the tip seal 77. Accordingly, inthe through hole 31 a, the tip seal 77 blocks communication between aninner space of the boss 67 communicating with the balancer chamber 14and an outer space of the boss 67.

[0026] The fixed scroll member 41 and the movable scroll member 45engage with each other by the respective spiral walls 63, 66 in thescroll chamber 15, while the distal end of the spiral wall 63 and thedistal end of the spiral wall 66 contact with the base plate 65 of themovable scroll member 45 and the base plate 61 of the fixed scrollmember 41, respectively. Accordingly, the base plate 61 and the spiralwall 63 of the fixed scroll member 41 and the base plate 65 and thespiral wall 66 of the movable scroll member 45 define compressionchambers 47 in the scroll chamber 15.

[0027] A self-rotation blocking mechanism 48 is provided between thebase plate 65 of the movable scroll member 45 and the center frame 31facing the base plate 65. The self-rotation blocking mechanism 48includes a plurality of cylindrical holes 48 a and a plurality of pins48 b (only one of them is shown in FIG. 1). The cylindrical holes 48 aare recessed in radially outer portions of the back surface 65 a of thebase plate 65 in the movable scroll member 45. The pins 48 b are buriedin an end surface 31 c of the center frame 31 and are loosely fittedtherein.

[0028] In the scroll chamber 15, a suction chamber 51 is defined betweenthe outer circumferential wall 62 of the fixed scroll member 41 and theoutermost circumferential portion of the spiral wall 66 of the movablescroll member 45. A suction passage 39 is formed in radially outerportions of the shaft support member 32, the shim 68 and the centerframe 31 for interconnecting the suction chamber 51 and the motorchamber 12.

[0029] A suction port 50 is formed in the cylindrical portion 23 of thefirst housing element 21 and is located to correspond with the motorchamber 12. The suction port 50 connects with an external conduit, whichfurther connects with an evaporator (not shown) of an externalrefrigerant circuit. The suction port 50 communicates with the motorchamber 12. Accordingly, relatively low pressure refrigerant gas fromthe external refrigerant circuit is introduced into the suction chamber51 through the suction port 50, the motor chamber 12 and the suctionpassage 39.

[0030] In the housing 11, a discharge chamber 52 is defined between thesecond housing element 22 and the fixed scroll member 41. A dischargeport 53 for communicating with the discharge chamber 52 is formed in thesecond housing element 22. The discharge port 53 connects with anexternal conduit, which further connects with a gas cooler (not shown)of the external refrigerant circuit. Accordingly, relatively highpressure refrigerant gas in the discharge chamber 52 is delivered to theexternal refrigerant circuit through the discharge port 53.

[0031] A discharge hole 41 a is formed through the center of the baseplate 61 of the fixed scroll member 41. The compression chamber 47 nearthe center communicates with the discharge chamber 52 through thedischarge hole 41 a. In the discharge chamber 52, a discharge valve 55constituted of a reed valve is arranged on the base plate 61 of thefixed scroll member 41 for opening and closing the discharge hole 41 a.The opening degree of the discharge valve 55 is regulated by a retainer56, which is fixedly arranged on the base plate 61 of the fixed scrollmember 41.

[0032] As the rotary shaft 33 is rotated by the electric motor 13, themovable scroll member 45 orbits around the axis (the axis L of therotary shaft 33) of the fixed scroll member 41 through the crankshaft43. At the moment, the self-rotation of the movable scroll member 45 isblocked by the self-rotation blocking mechanism 48, so that only theorbital movement of the movable scroll member 45 is permitted. Due tothe orbital movement of the movable scroll member 45, the compressionchambers 47 reduce in volume as the compression chambers 47 move fromthe radially outer side of the spiral walls 63, 66 of the respectivescroll members 41, 45 toward the center of the spiral walls 63, 66.Thus, relatively low pressure refrigerant gas introduced from thesuction chamber 51 to the compression chambers 47 is compressed. Thecompressed refrigerant gas is discharged to the discharge chamber 52through the discharge hole 41 a by pushing away the discharge valve 55.

[0033] The operation for adjusting back pressure of the movable scrollmember 45 will now be described.

[0034] As shown in FIG. 1, in the scroll chamber 15, a back pressurechamber 16 is located on the side of the back surface 65 a of the baseplate 65 of the movable scroll member 45. The base plate 65 and the boss67 of the movable scroll member 45 and the center frame 31 surround todefine the back pressure chamber 16. Communication between the backpressure chamber 16 and the balancer chamber 14 is blocked by the tipseal 77, which is interposed between the boss 67 of the movable scrollmember 45 and the contact portion 31 b of the center frame 31.

[0035] As shown in FIGS. 2 and 3A, in the back surface 65 a of the baseplate 65 of the movable scroll member 45, an annular groove 65 b foraccommodating a seal is recessed in radially outer portion relative tothe cylindrical recesses 48 a so as to surround the cylindrical recesses48 a. An annular seal member 75 constituted of a tip seal is fitted inthe groove 65 b. The back surface 65 a of the movable scroll member 45slidably and elastically contacts with an end surface 31 c of the centerframe 31 by the seal member 75. Namely, the seal member 75 is interposedat a clearance CL between the back surface 65 a of the movable scrollmember 45 and the end surface 31 c of the center frame 31. Communicationbetween the back pressure chamber 16 and the suction chamber 51 throughthe entire clearance CL is blocked by the seal member 75.

[0036] Incidentally, a maximum distance of the clearance CL between themovable scroll member 45 and the center frame 31, that is, a thrustclearance between the movable scroll member 45 and the center frame 31,is adjusted in an appropriate distance in such a manner that a shim 68having an appropriate thickness is selected from a plurality of shims 68having different thicknesses and is assembled to the clearance CL whenthe electric compressor is manufactured.

[0037] As shown in FIGS. 1 and 2, an introducing passage 76 is formed inthe base plate 65 of the movable scroll member 45 so as to extendthrough the base plate 65 in thickness. Two introducing passages 76 areprovided. The back pressure chamber 16 and a volume-reducing(compressing) compression chamber 47A, which is a relatively highpressure region, are interconnected through one introducing passage 76.The back pressure chamber 16 and a volume-reducing compression chamber47B, which is different from the compression chamber 47A, areinterconnected through the other introducing passage 76. The introducingpassages 76 are symmetrically located in the base plate 65 from eachother with an angle of 180 degrees with respect to the axis of thecrankshaft 43, and respectively open to the corresponding compressionchambers 47A, 47B.

[0038] A fixed throttle 76 a is arranged in each of the introducingpassages 76. In the movable scroll member 45, the back surface 65 a ofthe base plate 65 forms two accommodating recesses 65 c, with which theopening of each introducing passage 76 on the side of the back pressurechamber 16 communicates. A check valve 78 constituted of a reed valve isaccommodated in each of the accommodating recesses 65 c. The checkvalves 78 each permit refrigerant gas supplied from the compressionchambers 47A, 47B to the back pressure chamber 16, and block therefrigerant gas returned from the back pressure chamber 16 to thecompression chambers 47A, 47B.

[0039] As shown in FIGS. 2 and 3A, a portion 75 a for lowering sealingperformance (hereinafter, a seal lowering portion 75 a) relative to theother portion is provided for the seal member 75. The seal loweringportion 75 a is formed by splitting a portion of the annular sealmember. The back pressure chamber 16 and the suction chamber 75, whichis a relatively low pressure region, are interconnected through the seallowering portion 75 a of the seal member 75 in the clearance CL betweenthe movable scroll member 45 and the center frame 31. Incidentally, inFIG. 2, dimensions of the seal lowering portion 75 a (a split portion inthe seal member 75) are exaggeratedly illustrated for easierunderstanding. Actually, the seal lowering portion 75 a is formed by anextremely narrow clearance.

[0040] Incidentally, according to the present invention, a relativelyhigh pressure region means a region where relatively high pressurerefrigerant gas, which is compressed by the fixed scroll member 41 andthe movable scroll member 45, exists, while a relatively low pressureregion means a region where relatively low pressure refrigerant gas,which is yet to be compressed by the fixed scroll m ember 41 and themovable scroll member 45, exists.

[0041] As shown in FIG. 1, as pressure in the volume-reducingcompression chambers 47A, 47B rises to exceed pressure in the backpressure chamber 16 due to operation of the electric compressor, thecheck valve 78 opens so that the relatively high pressure refrigerantgas in the volume-reducing compression chambers 47A, 47B is introducedinto the back pressure chamber 16 through the respective introducingpassages 76. Accordingly, the pressure in the back pressure chamber 16rises so that force (back pressure force) F1 urging the movable scrollmember 45 toward the fixed scroll member 41 is applied based upon thepressure in the back pressure chamber 16. On the other hand, force(thrust load) F2 based upon the pressure in the compression chambers 47is applied to the movable scroll member 45 toward a direction to leavethe fixed scroll member 41. Accordingly, a position of the movablescroll member 45 relative to the center frame 31 is determined inaccordance with a balance between the force F1 and the force F2.

[0042] As exaggeratedly shown in FIG. 3A, for example, as the force F1becomes greater than the force F2 (F1>F2) due to an increase in thepressure in the back pressure chamber 16, the movable scroll member 45is displaced in a direction in which the back surface 65 a leaves theend surface 31 c of the center frame 31. Accordingly, sliding resistancebetween the back surface 65 a of the movable scroll member 45 and theend surface 31 c of the center frame 31 is reduced. In addition, whenthe force F1 becomes greater than the force F2 (F1>F2), the movablescroll member 45 is pressed against the fixed scroll member 41 so thatsealing performance of the compression chambers 47 improves.

[0043] As the movable scroll member 45 leaves the center frame 31 toincrease the clearance CL between the movable scroll member 45 and thecenter frame 31, the passing cross-sectional area of refrigerant gasincreases at the seal lowering portion 75 a of the seal member 75.Accordingly, the amount of refrigerant gas delivered from the backpressure chamber 16 to the suction chamber 51 increases so that thepressure in the back pressure chamber 16 falls to reduce the force F1.

[0044] As exaggeratedly shown in FIG. 3B, as the force F1 becomessmaller than the force F2 (F1<F2) due to a reduction in the pressure inthe back pressure chamber 16, the movable scroll member 45 is displacedin a direction in which the back surface 65 a approaches the end surface31 c of the center frame 31. Accordingly, sliding resistance between themovable scroll member 45 and the fixed scroll member 41 is reduced.

[0045] As the movable scroll member 45 approaches the center frame 31 toreduce the clearance between the movable scroll member 45 and the centerframe 31, the passing cross-sectional area of refrigerant gas reduces atthe seal lowering portion 75 a of the seal member 75. Accordingly, theamount of refrigerant gas delivered from the back pressure chamber 16 tothe suction chamber 51 reduces so that the pressure in the back pressurechamber 16 rises to increase the force F1.

[0046] Thus, the movable scroll member 45 varies the clearance CL(distance) between the back surface 65 a and the end surface 31 c of thecenter frame 31 in such a manner that the force F1 based upon thepressure in the back pressure chamber 16 becomes an appropriatemagnitude in a correspondence with the force F2 based upon the pressurein the compression chambers 47. The passing cross-sectional area of theseal lowering portion 75 a is thereby autonomously adjusted.Incidentally, in the preferred embodiment, in order to enhancecompression efficiency by improving sealing performance of thecompression chambers 47, the adjustment of the pressure in the backpressure chamber 16 is predetermined in such a manner that a state,where the force F1 applied to the movable scroll member 45 slightlyexceeds the force F2, is maintained for a relatively long time.

[0047] According to the preferred embodiment, the following advantageouseffects are obtained.

[0048] (1) The movable scroll member 45 varies the clearance CL betweenthe movable scroll member 45 and the center frame 31 in such a mannerthat the force F1 based upon the pressure in the back pressure chamber16 becomes an appropriate magnitude in a correspondence with the forceF2 based upon the pressure in the compression chambers 47. Thus, thepassing cross-sectional area of the seal lowering portion 75 a of theseal member 75 is autonomously adjusted. In comparison to a prior art inwhich an entire clearance CL between the movable scroll member 45 andthe center frame 31 is utilized as a passage for delivering refrigerantgas from the back pressure chamber 16 to the suction chamber 51, thesurfaces 31 c and 65 a respectively facing the movable scroll member 45and the center frame 31 need not be manufactured in high accuracy.Accordingly, the pressure in the back pressure chamber 16 isappropriately adjusted without an increase in cost for manufacturing theelectric compressor.

[0049] (2) The seal lowering portion 75 a for lowering sealingperformance of the seal member 75 is formed by splitting a portion ofthe annular seal member 75. Accordingly, the seal lowering portion 75 ais easily formed in the seal member 75.

[0050] (3) The shim 68 is interposed at a joint between the fixed scrollmember 41 fixed to the housing 11 and the center frame 31 also fixed tothe housing 11 for adjusting a thrust clearance between the movablescroll member 45 and the center frame 31. For example, in comparison tothe shim 68 interposed at a sliding portion between the movable scrollmember 45 and the center frame 31, the leakage of refrigerant gas at aportion where the shim 68 is interposed is prevented in the preferredembodiment. This leads to improving compression efficiency of theelectric compressor.

[0051] (4) The shaft support member 32, by which the rotary shaft 33 issupported through the bearing 35, is independently provided from thecenter frame 31, on which the movable scroll member 45 slides. Thebalancer chamber 14 is defined between the shaft support member 32 andthe center frame 31, and the balancer 44 a is accommodated in thebalancer chamber 14. For example, in comparison to a structure in whichthe shaft support member 32 is integrated with the center frame 31 asone component and the balancer 44 a is accommodated in the back pressurechamber 16 (This embodiment is not a departure from the presentinvention.), sealing of the back pressure chamber 16 becomes easy.

[0052] In other words, in a state of a comparative example, the rotaryshaft 33 is partially located in the back pressure chamber 16, so thatthe back pressure chamber 16 need be sealed by a lip seal. The lip seal,in view of its characteristic, tightly fastens the rotary shaft 33 forperforming desirable sealing performance. As a result, power loss of therotary shaft 33 increases, and appropriate seal of the back pressurechamber 16 and a reduction in power loss are not performed at the sametime.

[0053] Incidentally, in the above comparative example, as disclosed inthe Unexamined Japanese Patent Publication No. 2000-249086, a pocket forback pressure is recessed in the back surface 65 a of the movable scrollmember 45, and the back pressure chamber is formed by covering thepocket for applying back pressure with the center frame 31. Thus, therotary shaft 33 need not be sealed by the lip seal. However, in thisstate, since the suction pressure is partially applied to the backsurface of the movable scroll member 45 other than the pressure in theback pressure chamber, it becomes complicated to appropriately setfunction for adjusting back pressure. Additionally, the pocket forapplying back pressure need be recessed in the movable scroll member 45,so that cost for manufacturing increases.

[0054] The relatively high pressure region includes two volume-reducingcompression chambers 47A, 47B. Two introducing passages 76 are provided.One compression chamber 47A and the back pressure chamber 16 areinterconnected through one introducing passage 76, while the othercompression chamber 47B and the back pressure chamber 16 areinterconnected through the other introducing passage 76. Thus,relatively high pressure refrigerant gas is supplied from twocompression chambers 47A, 47B to the back pressure chamber 16, so thatthe inclination of the movable scroll member 45 due to a reduction inpressure in the compression chambers 47A, 47B by supplying therelatively high pressure refrigerant gas is prevented.

[0055] Namely, for example, when one compression chamber 47A onlysupplies relatively high pressure gas to the back pressure chamber 16(this embodiment is not a departure from the present invention),pressure in the compression chamber 47A is reduced by supplying therelatively high pressure refrigerant gas to the back pressure chamber16, while pressure in the other compression chamber 47B, which islocated on a side opposite to the compression chamber 47A relative tothe axis (the axis of the crankshaft 43) of the movable scroll member45, is not reduced. Accordingly, force applied to the movable scrollmember 45 based upon pressure in the compression chambers 47A, 47Bbecomes imbalance on each side relative to the axis, so that the movablescroll member 45 tends to incline relative to the axis of the movablescroll member 45.

[0056] (6) Carbon dioxide is employed as refrigerant for therefrigeration cycle. As described in the prior art, when carbon dioxiderefrigerant is employed, passing cross-sectional area of a refrigerantgas passage between the back pressure chamber 16 and the suction chamber51 need be much narrower at the maximum than that when fluorocarbonrefrigerant is employed. Such a setting is easily handled by partiallylowering sealing performance of the seal member 75 with low cost.

[0057] The present invention is not limited to the embodiment describedabove but may be modified into the following alternative embodiments.

[0058] In alternative embodiments to the above preferred embodiment, thebalancer chamber 14 is defined as a relatively low pressure region,while the tip seal 77 for separating the balancer chamber 14 from theback pressure chamber 16 is defined as a seal member. As shown in FIG.4, the tip seal 77 is partially split to form a seal lowering portion 77a for lowering sealing performance, and the back pressure chamber 16 andthe balancer chamber 14 are interconnected through the seal loweringportion 77 a.

[0059] In this state, as the operation being described with reference toFIGS. 1 and 4, for example, as the force F1 becomes greater than theforce F2 (F1>F2) due to a rise in the pressure in the back pressurechamber 16, the movable scroll member 45 is displaced in a direction inwhich the distal end surface of the boss 67 leaves the contact portion31 b of the center frame 31. Accordingly, a clearance between the distalend surface of the boss 67 and the contact portion 31 b of the centerframe 31 increases, so that the passing cross-sectional area forrefrigerant gas increases at the seal lowering portion 77 a of the tipseal 77. The amount of refrigerant gas delivered from the back pressurechamber 16 to the balancer chamber 14 increases, and the pressure in theback pressure chamber 16 falls to reduce the force F1.

[0060] As the force F1 becomes smaller than the force F2 (F1<F2) due toa reduction in the pressure in the back pressure chamber 16, the movablescroll member 45 is displaced in a direction in which the distal end ofthe boss 67 approaches the contact portion 31 b of the center frame 31.Accordingly, a clearance between the distal end surface of the boss 67and the contact portion 31 b of the center frame 31 reduces, so that thepassing cross-sectional area for refrigerant gas reduces at the seallowering portion 77 a of the tip seal 77. The amount of refrigerant gasdelivered from the back pressure chamber 16 to the balancer chamber 14reduces, and the pressure in the back pressure chamber 16 rises toincrease the force F1.

[0061] According to another embodiment, the same advantageous effects,such as appropriate adjustment of pressure in the back pressure chamber16 with a relatively low-cost structure, are obtained.

[0062] As shown in FIG. 5, in addition to the structure described in thepreferred embodiment, the back pressure chamber 16 and a relatively lowpressure region (the balancer chamber 14) are interconnected not throughthe seal lowering portion 75 a but through another passage 81. Adifferential pressure regulating valve 82 is arranged in the passage 81for opening when differential pressure between the back pressure chamber16 and the balancer chamber 14 is equal to or greater than apredetermined value. Incidentally, the differential pressure regulatingvalve 82 includes a spherical valve body 82 a, a coil spring 82 b and aspring seat 82 c. The pressure in the back pressure chamber 16 and thepressure in the balancer chamber 14 are respectively applied to thefront side and the rear side of the valve body 82 a. The coil spring 82b urges the valve body 82 a in a direction to close the valve.

[0063] As described in the preferred embodiment, the passingcross-sectional area of the seal lowering portion 75 a is adjusted inresponse to a balance between the force F1 based upon the pressure inthe back pressure chamber 16 and the force F2 based upon the pressure inthe compression chambers 47. Namely, in the embodiment of FIG. 5, thepressure in the back pressure chamber 16 is adjusted by utilizing twovalves (the seal lowering portion 75 a and the differential pressureregulating valve 82) each having different characteristic. Accordingly,a region where only one of the valves 75 a and 82 cannot appropriatelyadjust pressure may be mutually covered by combination with the other ofthe valves 82 and 75 a. Thus, the pressure in the back pressure chamber16 is further appropriately adjusted.

[0064] In the preferred embodiment, one portion of the annular sealmember 75 is split to form the seal lowering portion 75 a. Inalternative embodiments, a plurality of portions of a seal member, suchas two, three, four, five or six portions, is split to form portion forlowering sealing performance at plural portions of the seal member.

[0065] In the preferred embodiment, the seal lowering portion 75 a isformed by partially splitting the annular seal member 75. In alternativeembodiments, the annular shape of the seal member is maintained, while agroove is partially formed in the seal member. Thus, a seal loweringportion for lowering sealing performance is formed.

[0066] In the preferred embodiment, two volume-reducing compressionchambers 47A, 47B independently communicate with the back pressurechamber 16 through the respective introducing passages 76. Inalternative embodiments, two introducing passages 76, which respectivelyextend from two compression chambers 47A, 47B, are integrated on the wayand the integrated one introducing passage communicates with the backpressure chamber 16. Thus, only one portion of the movable scroll member45 (the base plate 65) is recessed to form the accommodating recess 65c, and the only one check valve 78 is required. Accordingly, cost formanufacturing the electric compressor is reduced.

[0067] In the preferred embodiment, relatively high pressure refrigerantgas is introduced from the volume-reducing compression chambers 47A, 47Bto the back pressure chamber 16. In alternative embodiments, thecompression chamber 47 near the center (the compression chamber 47completes compression) or the discharge chamber 52 is defined as arelatively high pressure region, while the upstream portion of theintroducing passage 76 communicates with the relatively high pressureregion, so that the high pressure refrigerant gas, which is higher inpressure than the refrigerant gas in the volume-reducing compressionchambers 47A, 47B, is introduced to the back pressure chamber 16.

[0068] In the preferred embodiment, a scroll compressor is embodied asthe electric compressor. The scroll compressor is not limited to theelectric compressor. In alternative embodiments, a scroll compressordriven by an engine of a vehicle, a hybrid type scroll compressor havingan electric motor and an engine as drive sources, may be employed.

[0069] Therefore, the present examples and embodiments are to beconsidered as illustrative and not restrictive, and the invention is notto be limited to the details given herein but may be modified within thescope of the appended claims.

What is claimed is:
 1. A scroll compressor comprising: a housing including a fixed wall, the housing defining a relatively high pressure region and a relatively low pressure region; a fixed scroll member having a base plate and a spiral wall extending from the base plate, the fixed scroll member being fixedly connected to the housing; a movable scroll member having a base plate and a spiral wall extending from the base plate, the movable scroll member being engaged with the fixed scroll member, whereby a compression chamber is defined between the fixed scroll member and the movable scroll member, the compression chamber progressively reducing in volume by orbiting the movable scroll member relative to the fixed scroll member, thus compressing gas; a back pressure chamber defined in the housing on a back surface side of the base plate of the movable scroll member between the movable scroll member and the fixed wall; an introducing passage interconnecting the back pressure chamber and the relatively high pressure region; and a seal member provided on one of the movable scroll member and the fixed wall for sealing the back pressure chamber as being slidable on the other of the movable scroll member and the fixed wall, the seal member including a seal lowering portion for lowering sealing performance, the seal lowering portion interconnecting the back pressure chamber and the relatively low pressure region.
 2. The scroll compressor according to claim 1, wherein the seal member has an annular shape, the seal lowering portion being formed by partially splitting the seal member.
 3. The scroll compressor according to claim 1, wherein the movable scroll member is accommodated in a scroll chamber, which is defined by connecting the fixed scroll member and the fixed wall at a joint, the scroll compressor further comprising: a shim interposed at the joint between the fixed scroll member and the fixed wall for adjusting a thrust clearance between the movable scroll member and the fixed wall.
 4. The scroll compressor according to claim 1, further comprising: a rotary shaft including a crankshaft for supporting the movable scroll member; a shaft support member fixedly connected to the fixed wall on a side opposite to the movable scroll member in the housing, the shaft support member rotatably supporting the rotary shaft, a balancer chamber being defined between the fixed wall and the shaft support member; and a balancer provided for the crankshaft, the balancer being accommodated in the balancer chamber.
 5. The scroll compressor according to claim 1, wherein the back pressure chamber communicates with the relatively low pressure region through a passage other than the seal lowering portion, the scroll compressor further comprising: a differential pressure regulating valve arranged in the passage for opening the passage when pressure differential between the back pressure chamber and the relatively low pressure region is equal to or higher than a predetermined value.
 6. The scroll compressor according to claim 1, wherein the relatively high pressure region includes two volume-reducing compression chambers, which respectively communicate with the back pressure chamber through the introducing passage.
 7. The scroll compressor according to claim 6, wherein two volume-reducing compression chambers respectively communicate with the back pressure chamber through the respective independent introducing passages.
 8. The scroll compressor according to claim 1, wherein the introducing passage is formed in the base plate of the movable scroll member.
 9. The scroll compressor according to claim 1, wherein carbon dioxide is employed as refrigerant of the refrigeration cycle.
 10. The scroll compressor according to claim 1, wherein the compressor is driven by an electric motor. 